Crowns are commonly used as adjusting members for mechanical watches. Mounted on a tube which is driven or screwed into the middle part of the watch case, crowns are assembled at the end of a winding or control stem, and can take several distinct axial positions in which they can execute various types of functions, such as for example winding the barrel of the watch, setting the time, adjusting the date etc.
Screw-in crowns are commonly used for watches in order to improve the sealing of watches on their winding or control stem. This type of crown has the peculiarity of having to be in an unscrewed position to be capable of being actuated, in which the axial position of the crown can be changed to define an adjustment mode. In the screwed-in position, the crown is locked onto a tube, which is fixed inside the middle part and which preferably has a bulged part at the base of the portion thereof projecting outside the middle part of the case, in order to compress a sealing gasket, thereby improving the sealing of the watch. The screwed-in position is therefore the normal position when the watch is being worn and which has the best sealing properties, suitable, in particular, for use during aquatic activities, such as deep sea diving.
There exist several known manufacturing and assembling methods for assembling these screw-in crowns onto the middle part of a watch. There even exist angular orientation adjustment devices for placing the crown in a determined position relative to the case after the crown has been screwed-in, when there is a marking affixed to the end surface of the crown. This is the case, for example when the crowns are fitted to luxury and high quality goods.
Most crowns, regardless of whether or not they are screwed-in and orientable, generally include a cap formed by a cover on the top surface of which a trademark or logo can be affixed, and a lateral skirt inside which the securing tube is housed. To guarantee the sealing of this type of crown with respect to the tube, one or more sealing gaskets are provided on the lower end of the skirt, and are radially compressed between the external surface of the tube and the skirt, and covered by means of a crimped or driven-in ring. These covering rings, which are used to hold the sealing gasket axially when the crown is operated, are also commonly called “deck rings”.
One drawback of these crowns is that sometimes it is impossible to replace a worn sealing gasket where the gasket is not accessible laterally when the crown is dismantled because the deck ring is permanently fixed to the bottom surface of the skirt of the crown. Consequently, during an after-sales service, for example, it may be necessary to replace the entire crown when its sealing properties deteriorate over time, which is very expensive.
EP Patent No. 0655664 proposes an alternative solution to deck rings for holding the sealing gasket of a crown-push button compressed against a guide tube by using an open, resilient, retaining ring engaged in a groove in the bottom face of the crown. These open resilient rings, also called circlips, are often employed as stop members for assembling and holding components in grooves about an arbour for larger sized parts, where the circlips are easy to handle using pliers which engage in holes at the ends thereof used for the assembly and removal of the circlips. However, the very reduced size of a timepiece crown, which is at most barely a few millimeters, makes the crown very difficult to handle, even simply to assemble, and particularly inconvenient for any subsequent dismantling operation. Moreover, the particular shape of the circlip requires a groove to be arranged in the bottom end of the crown skirt with a beak forming an axial retaining surface, as provided for in the invention disclosed by EP Patent No. 0655664, intended to prevent the circlip from being unintentionally wrenched out. This complicates the machining of the crown and therefore makes it more expensive to manufacture.